[llvm] [AArch64] Cap upper-bound unrolling of loops with uncomputable trip counts (PR #205102)

[Igor Kirillov via llvm-commits]

igogo-x86 wrote:

@david-arm [This comment](https://github.com/llvm/llvm-project/pull/208500#issuecomment-5093702705) shows the extra we would have to put into this patch if we don't land #208500 

https://github.com/llvm/llvm-project/pull/205102